"When they tried to come back they weren't in a very good position because we were up there with the top two boats," Robinson said, revealing all sailors had the opportunity before the start to have a test sail of sorts.
But "clear air", which is the opposite effect of slip streaming in cycling, is essential to avoid sailing in "wind shadows".
Hong Kong reps Ashley Smith/Adam Kingston crossed fourth and Whangarei pair Rob Ward/Bruce Yovich, of Onerahi YC, were fifth.
Robinson won a race at the 2011 world at Hayleigh, in southwest England, with fellow Napier club member James Sandall, of Wairoa, to finish 28th overall.
He described the 5-8 knots wind yesterday as "challenging" but small swells made it manageable.
He and Zorn have had little time racing together but the rapport has been great.
"It's always been from the first day," he said after they competed at last year's nationals. "His father, [the late Russell Zorn], was an excellent sailor in different classes of boats and was the race officer in the 1982 here and was a life member."
Business owner Robinson considered himself lucky to have David Zorn's nous to be in 21st place provisionally.
"At 21st I'd be a very, very happy chap when I look at the sort of people ahead of us it'll be very challenging with such outstanding sailors," he said with a laugh.
Australians are in the top three overall provisionally. David Yu/Chris Nelson on 13 points with Matthew Owen/Andrew Reed while husband-and-wife combo Nick/Janet Jerwood are third (15).
Britons make up the next tier - McKee/Hartland (19), Jeremy Davy/Martin Huett (24), Goacher/Harper (28).
Racing is expected to resume in similar conditions at 1pm today along the Ahuriri waterfront.